This invention relates to a waveform normalizer for an electronic musical instrument, which normalizes a waveform obtained by storing an externally supplied sound signal to generate a waveform suited as a tone waveform signal.
Heretofore, there have been developed various electronic musical instruments which have a sampling function of receiving and digitally recording an externally supplied sound signal and reading out the recorded sound signal as a waveform signal to be provided as a note signal.
Electronic musical instruments having such a sampling function are also disclosed in patent applications U.S. Ser. Nos. 760,290 filed on July 29, 1985, 760,291 filed on July 29, 1985 and now U.S. Pat. No. 4,667,556, U.S. application based on Japanese patent application Nos. 60-200259, 60-201301 and U.S. application based on Japanese patent application Nos. 60-202698, 60-205516, 60-207147 and 60-207150, these U.S. applications being assigned to the assignee of this invention.
In these prior art electronic musical instruments, the sound signal is directly sampled and stored.
As is well known in the art, a sound has an instantaneously changing level, and in the field of electronic musical instruments it is thought that the waveform of an original sound is superimposed on a waveform called envelope to generate a musical tone. The envelope has an amplitude changing with the lapse of sounding time. In the prior art electronic musical instrument with a sampling function, a waveform signal including the envelope is usually stored.
Therefore, when a sampled tone including envelope is reproduced at a desired pitch for musical performance, the rate of reading of the waveform of the sampled tone varies with the pitch, so that the envelope time also varies with the pitch, that is, it is impossible to obtain a uniform envelope time.
In some case, a digitally recorded waveform signal is read out as a note signal at a predetermined rate to be converted into an analog signal before providing an envelope thereto through a voltage controlled amplifier (VCA) or the like. In this case, the resultant signal is a combination of the initial envelope and subsequently added envelope in superimposition thereon, so that it is difficult to obtain sufficient envelope control.
Further, when a continued tone is to be generated through a loop function by repeatedly reading out a particular portion of a waveform signal like that noted above, a level difference appears outstandingly at the juncture between adjacent waveforms in case when the waveform signal includes an envelope of attenuating type. Such level difference leads to a click or like noise. Thus, such a loop function can be obtained only for a short portion of the stored waveform.